Create git-tag on deploy

Do you guys think it would be useful to create tags every time you deploy?

for example, if you run

```
heroku deploy develop
```

it creates the tag `deploy-develop-YYYY-MM-DD-HH-MM`

or something like that then you can do diff between `HEAD` and the last deploy tag

I included the name of the brach as well, in this way we can track in git deployments to staging and production